We have a lot of tapes LTO4 from a older Microsoft DPM installation that will be used in a new VBR installation.
After do the erase ( short or long ) the tape in the Free Pool show the correct capacity and free space ( 780GB ).
When a tape Job is started, in 450GB it request another tape because the first is full.

The LTO4 is a 800GB native capacity. I think that this capacity need to the reached ( 780GB after the format ).

We also did the Tape Erase with the vendor utility ( more than 03 hours to complete ) and the result is the same.

Veeam B&R works with the size revived from tape via tape device. Looks like the EOT (end of tape) marker for this particular media was set at 780GB. You can check the actual capacity via tape vendor utilities. Thanks.